Calcium Supplementation for a Healthy Weight (CaSHeW)

Inclusion Criteria: * Men or women, between 18 and 65 years of age, who are capable of providing informed consent. * BMI of 25 to 35 kg/m2 * Non-smoker (for at least 6 months). * In good health, as determined by the principal investigator based on medical history and physical examination. * Clinical laboratory evaluations (including Biochemistry, Hematology, Urinalysis) within the reference range for the test laboratory, unless deemed not clinically significant by the Investigator. * Because of the calorie-restricted diet and radiation exposure from the CT scan, females will be non-pregnant, non-lactating, and either post-menopausal for at least 1 year, surgically sterile for at least 3 months, or be willing to use an approved method of contraception (which may include use of abstinence; non-hormonal intrauterine device with spermicide; female condom with spermicide; diaphragm with spermicide; cervical cap with spermicide; oral or transdermal hormonal contraceptives; a condom with spermicide by the sexual partner; or a sterile sexual partner) from 35 days prior to study entry (i.e., Day -1) until 30 days following Study Completion. For all females, the pregnancy test result must be negative at the screening visit and at visits when a CT scan will be done. * Ability to comprehend and willingness to sign the Informed Consent Form for this study. * Ability to comply with study restrictions regarding diet and exercise * Stable weight (+ 5%) for at least 3 months prior to study entry. Exclusion Criteria: * Diabetes mellitus * History or clinical manifestations of significant metabolic, hepatic, renal, hematological, pulmonary, cardiovascular, gastrointestinal, urological, neurological, or psychiatric disorders which in the opinion of the investigator would be expected to interfere with the study or increase risk to the subject. * Participation in any other investigational diet study within 90 days prior to study entry. * History of a medical or psychological condition or social circumstances that would impair the subject's ability to participate reliably in the study. * Use within the last six months of medications that can result in significant weight gain or weight loss, including antipsychotics, selective serotonin reuptake inhibitors, anti-epileptic drugs, appetite-suppressants such as phentermine and sibutramine, and the lipase-inhibitor orlistat. * Active eating disorder * History of alcoholism or substance abuse within 5 years prior to study entry. * Use of a dietary supplement or medication that decreases calcium absorption * History of kidney stone, hyperparathyroidism or sarcoidosis * High calcium intake (more than 2 servings of dairy products per day or taking calcium supplements \> 3x/wk ) for 1 month prior to study start date and for duration of study. (If participant is taking calcium supplement \> 3x/wk or more than 2 servings of dairy products per day, they are eligible to participate if they agree to stop for 1 month prior to study start date and for the duration of the study. Participants will similarly be asked to stop multivitamins as the majority of these supplements contain calcium.)